Usefulness of the "not in" operator

[Chris Angelico]

On Sun, Oct 9, 2011 at 2:16 AM, Dave Angel <d at davea.name> wrote:
> You should say
>    "... parenthesis are not necessary ("not" has LOWER precedence than
> "in")."
>

Is "are not" an operator in English, or should this be "not
parentheses are necessary"?

ChrisA